Centerless grinders are well known and conventionally comprise a base on which a rotary grinding wheel is mounted for rotation in one direction about a substantially horizontal axis and a regulating wheel which confronts, but is spaced from, the grinding wheel and which is mounted on the base for rotation in the same direction about an axis. The axis of rotation of the regulating wheel frequently is inclined somewhat to the horizontal so as to enable a workpiece accommodated in the gap between the grinding and regulating wheels to be fed automatically through such gap as the workpiece is ground.
It is conventional to mount the grinding wheel, the regulating wheel, or both, for adjustment toward and away from one another and thereby vary the gap between such wheels. Adjustability of the gap is necessary so as to enable the grinding machine to accommodate workpieces of different diameters and also to compensate for wear of the grinding wheel due to attrition and dressing. Although conventional centerless grinders include adjusting mechanisms for these purposes, adjusting means should be provided to compensate for changes in the peripheral speed of the grinding wheel because of the reduction in its diameter due to such attrition and dressing. It is believed that some centerless grinders provide one, or possibly two, input driving speeds for the grinding wheel or regulating wheel, but in those instances in which the grinder is used to grind workpieces to extremely small tolerances, such limited speed adjustments are inadequate.
Apparatus constructed in accordance with the invention overcomes the prior art inadequacy by providing an infinitely adjustable drive mechanism for the regulating wheel.
It is not uncommon for the coupling between the regulating wheel and its driving means to comprise a complex, geared transmission. Since the grinding wheel and the regulating wheel are driven in the same direction, and since the workpiece is positioned in the gap between the two wheels, and since the grinding wheel conventionally is the larger wheel and has a greater peripheral speed, the workpiece transmits a force from the grinding wheel to the regulating wheel that attempts to accelerate the latter. This phenomenon often is referred to as "back driving" and subjects the conventional geared transmission to severe strain and consequent wear. The adverse effect of the grinding wheel's tending to drive the regulating wheel via the workpiece is particularly noticeable in those instances in which workpieces are presented to the grinder in spaced intervals. Thus, when a ground workpiece is removed from the gap between the wheels, the speed of the regulating wheel may decrease, but when a fresh workpiece is introduced to the gap there is an immediate shock imposed on the regulating wheel drive mechanism due to the grinding wheel's attempting to accelerate the regulating wheel. As a consequence the speed of rotation of the regulating wheel varies, with adverse results on the finish of the workpiece, and the drive mechanism is subjected to wear.
Apparatus constructed in accordance with the invention overcomes these disadvantages of the known grinders by utilizing a regulating wheel drive mechanism which positively resists any tendency to be the regulating wheel.